The present invention relates to an apparatus for measuring the temporal correlation of photons, neutrons and other fundamental particles.
There has been known an apparatus for measuring the temporal correlation of photons detected from incident light.
The operating principle of the apparatus for measuring photon's temporal correlation is shown in FIG. 1. A photon beam is divided by a beam splitter 71 and the resulting two beams are directed into detectors 72 and 73. By changing the time-dependent parameter for each detector, the temporal correlation of photons can be measured with a correlator 74. Each of the detectors 72 and 73 comprises a photomultiplier tube, a semiconductor detector or the like.
If the respective distances from the beam splitter 71 to the detectors 72 and 73 are l.sub.1 and l.sub.2, the difference in arrival time .tau.(the difference between the times at which photons arrive at the detectors 72 and 73) is expressed as: EQU .tau.=(l.sub.1 -l.sub.2)/c (1)
where c is the velocity of light. By measuring the probability that photons are simultaneously detected with detectors 72 and 73, the temporal correlation of photons within a time interval of .tau. can be determined.
FIG. 2 shows schematically a conventional apparatus for measuring temporal correlation using a single detector, or a photomultiplier tube 80. A photon passing through light attenuating filters 82 and a pinhole 81 is detected with the detector 80, for example a photomultiplier tube and the signal line after the detection is divided into two lines, one of which is delayed for determining the temporal correlation of photon with a correlator 83.
With the conventional temporal correlation measuring an apparatus as described above, photons to be measured are admitted into the detectors 72 and 73 or detector 80 in a direct way, namely, sequentially on a time basis. In order to obtain temporal correlation for a very short time difference of the order of subnanoseconds with this mechanical arrangement, not only the detectors 72 and 73 or detector 80 but also the correlator 74 or 83 is required to have high-speed response characteristics for providing a high time-resolving capability. However, in the conventional technology, since the detectors 72 and 73 or detector 80 comprises a photomultiplier tube or semiconductor detector, the response speed cannot be made faster than 10 picoseconds.
Further there also is a limit on the efforts that can be made to realize high-speed response with the circuits constituting the correlator 74 or 83.
As described above, the conventional temporal correlation measuring apparatus has a limited capability for determining temporal correlation for a very short time difference with high temporal resolution.